Curved Wafer Processing Method and Apparatus

ABSTRACT

An apparatus for and a method of forming a semiconductor structure is provided. The apparatus includes a substrate holder that maintains a substrate such that the processing surface is curved, such as a convex or a concave shape. The substrate is held in place using point contacts, a plurality of continuous contacts extending partially around the substrate, and/or a continuous ring extending completely around the substrate. The processing may include, for example, forming source/drain regions, channel regions, silicides, stress memorization layers, or the like.

This application is divisional application of and claims the benefit ofU.S. patent application Ser. No. 13/404,819, filed Feb. 24, 2012,entitled “Curved Wafer Processing Method and Apparatus,” whichapplication is hereby incorporated herein by reference in its entirety.

BACKGROUND

Reduction of the size and the inherent features of semiconductor devices(e.g., a metal-oxide semiconductor field-effect transistor) have enabledcontinued improvement in speed, performance, density, and cost per unitfunction of integrated circuits over the past few decades. In accordancewith a design of the transistor and one of the inherent characteristicsthereof, modulating the length of a channel region underlying a gatebetween a source and drain of the transistor alters a resistanceassociated with the channel region, thereby affecting performance of thetransistor. More specifically, shortening the length of the channelregion reduces a source-to-drain resistance of the transistor, which,assuming other parameters are maintained relatively constant, may allowan increase in current flow between the source and drain when asufficient voltage is applied to the gate of the transistor.

To further enhance the performance of metal-oxide semiconductor (MOS)devices, stress may be introduced in the channel region of a MOStransistor to improve carrier mobility. Generally, it is desirable toinduce a tensile stress in the channel region of an n-typemetal-oxide-semiconductor (NMOS) device in a source-to-drain direction,and to induce a compressive stress in the channel region of a p-typemetal-oxide-semiconductor (PMOS) device in a source-to-drain direction.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present embodiments, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1-5 are cross-sectional views of intermediate stages in themanufacture of a device using a convex processing surface in anembodiment;

FIGS. 6 and 7 are cross-sectional views of intermediate stages in themanufacture of a device using a concave processing surface in anembodiment;

FIG. 8 is a cross-sectional view of an intermediate stage in themanufacture of a device using a convex processing surface in anembodiment;

FIG. 9 is a cross-sectional view of an intermediate stage in themanufacture of a device using a concave processing surface in anembodiment;

FIG. 10 is a cross-sectional view of an intermediate stage in themanufacture of a device using a convex processing surface in anembodiment;

FIG. 11 is a cross-sectional view of an intermediate stage in themanufacture of a device using a concave processing surface in anembodiment;

FIG. 12 is a cross-sectional view of an intermediate stage in themanufacture of a device using a convex processing surface in anembodiment;

FIG. 13 is a cross-sectional view of an intermediate stage in themanufacture of a device using a concave processing surface in anembodiment;

FIG. 14 illustrates a curvature of a processing surface in anembodiment;

FIGS. 15A1-15D2 illustrate different curvatures that may be used invarious embodiments;

FIGS. 16A1-16E illustrate different types of holders that may be used invarious embodiments; and

FIGS. 17A-17B illustrate a use of a stress film to form a curvedprocessing surface.

DETAILED DESCRIPTION

The making and using of the present embodiments are discussed in detailbelow. It should be appreciated, however, that the present disclosureprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use respectiveembodiments, and do not limit the scope of the present disclosure.

FIGS. 1-5 illustrate a method for fabricating a semiconductor devicehaving a strained channel region in accordance with an embodiment.Referring first to FIG. 1, a substrate 100 having gate structure 102formed thereon is shown in accordance with an embodiment. The substrate100 may comprise bulk silicon, doped or undoped, or an active layer of asemiconductor-on-insulator (SOI) substrate. Generally, an SOI comprisesa layer of a semiconductor material, such as silicon, formed on aninsulator layer. The insulator layer may be, for example, a buried oxide(BOX) layer or a silicon oxide layer. The insulator layer is provided ona substrate, such as a silicon or glass substrate. Other substrates,such as a multi-layered or gradient substrate may also be used. Thesubstrate may alternatively be a Ge substrate, a SiGe substrate, a groupIII-V, II-VI substrate, or the like.

The gate structure 102 may comprise a gate insulator layer 104 and agate electrode 106. The gate insulator layer 104 may be formed of ahigh-K dielectric material, such as silicon oxide, silicon oxynitride,silicon nitride, an oxide, a nitrogen-containing oxide, a combinationthereof, or the like. Other examples of such materials include aluminumoxide, lanthanum oxide, hafnium oxide, zirconium oxide, hafniumoxynitride, or combinations thereof Other embodiments may utilizespacers (not shown) formed alongside the gate structure to protect thegate structure during processing.

In an embodiment in which the gate insulator layer 104 comprises anoxide layer, the gate insulator layer 104 may be formed by any oxidationprocess, such as wet or dry thermal oxidation in an ambient comprisingan oxide, H₂O, NO, or a combination thereof, or by chemical vapordeposition (CVD) techniques using tetra-ethyl-ortho-silicate (TEOS) andoxygen as a precursor. Other methods (e.g., ALD) and materials may beused.

The gate electrode 106 may comprise a conductive material, such as ametal (e.g., tantalum, titanium, molybdenum, tungsten, platinum,aluminum, hafnium, or ruthenium), a metal silicide (e.g., titaniumsilicide, cobalt silicide, nickel silicide, or tantalum silicide), ametal nitride (e.g., titanium nitride or tantalum nitride), dopedpoly-crystalline silicon, other conductive materials, or a combinationthereof. In one example, amorphous silicon is deposited andrecrystallized to create poly-crystalline silicon (poly-silicon). In anembodiment in which the gate electrode is poly-silicon, the gateelectrode 106 may be formed by depositing doped or undoped poly-siliconby low-pressure CVD (LPCVD).

The gate insulator layer 104 and the gate electrode 106 may be patternedby photolithography techniques. Generally, photolithography involvesdepositing a photoresist material, which is then masked, exposed, anddeveloped. After the photoresist mask is patterned, an etching processmay be performed to remove unwanted portions of the gate dielectricmaterial and the gate electrode material to form the gate structure 102as illustrated in FIG. 1. In an embodiment in which the gate electrodematerial is poly-crystalline silicon and the gate dielectric material isan oxide, the etching process may be a wet or dry, anisotropic orisotropic, etch process.

FIG. 1 further illustrates recesses 110 formed on opposing sides of thegate structure 102. As discussed in greater detail below, astress-inducing layer will be epitaxially grown along the bottom of therecesses 110. In an embodiment, the recesses 110 may be etched by, forexample, HBr/O₂, HBr/Cl₂/O₂, or SF₆/Cl₂ plasma. One skilled in the artwill realize that the dimensions provided throughout the description aremerely examples, and the dimensions may vary with the scaling of thetechnology used for forming the integrated circuits.

Referring now to FIG. 2, there is shown the substrate 100 attached to asubstrate holder 212 in accordance with an embodiment. The holder 212 isconfigured to hold a substrate, such as the substrate 100, such that asurface of the substrate is curved. For example, in the embodimentillustrated in FIG. 2, the holder 212 clasps the substrate 100 such thata processing surface of the substrate 100 exhibits a convex shape. Inthis manner, the width of the recesses 110 increases. As explained ingreater detail below, an epitaxial layer will be grown in these recesseswhile the recesses are expanded. After the epitaxial layer is grown, thesubstrate is released from the holder, allowing the substrate 100 toreturn to, or near to, the original shape of the substrate 100, e.g.,return to planar or near-planar.

FIG. 3 illustrates the formation of stress-inducing regions 314 alongthe bottoms of the recesses 110. The material of the stress-inducingregions 314 is selected such that a lattice mismatch exists between thematerial of the stress-inducing regions 314 and the material of thesubstrate 100. One of ordinary skill in the art will also appreciatethat the type of materials may be varied depending upon the type ofdevice being formed. For example, in forming a PMOS device using asilicon substrate, the stress-inducing regions 314 may be formed ofSiGe, which has a larger lattice structure than the silicon substrate.The lattice structure of the SiGe stress-inducing regions 314 causes acompressive stress, indicated by arrows 316, in the channel region,thereby increasing the hole mobility. SiGe stress-inducing regions 314may be epitaxially grown in a selective epitaxial growth (SEG) processsuch as CVD using Si-containing gases and Ge-containing gases, such asSiH₄ and GeH₄, respectively, as precursors. Masks may be used to limitthe epitaxial growth regions.

When released, the stress-inducing regions 314 may exert a compressivestress in the channel region greater than that obtained using similarprocesses and materials on a planar wafer, at least partially due to theepitaxial growth on the curved surface increasing the volume of therecesses. The larger compressive stress is indicated in FIG. 4 by largerarrows 418, as compared to the smaller compressive stress indicated bythe smaller arrows 316 in FIG. 3.

FIG. 5 illustrates formation of silicide regions 518 in accordance withan embodiment. The embodiment illustrated in FIG. 5 may be usedindividually or with other embodiments within the scope of the currentdisclosure. Similar to the formation of the stress-inducing regions 314discussed above with reference to FIG. 3, the formation of the silicideregions 518 may also be performed while the surface of the substrate 100is in a curved configuration. Generally, the silicide regions 518 may beformed to decrease contact resistance between the source/drain regionsand contact vias extending through an overlying dielectric layer. Thesilicide regions 518 may be formed by blanket depositing a thin layer ofmetal, such as nickel, platinum, cobalt, and combinations thereof andannealing, such as a rapid thermal anneal, thereby causing the siliconto react with the metal where contacted. After the reaction, a layer ofmetal silicide is formed. The un-reacted metal may then be removed. Itis believed that forming the silicide regions 518 while the substrate100 is in a curved configuration helps reduce or avoid stress relaxationof the channel region during processing. In an embodiment, the silicideregion 518 may be formed after the processing illustrated in FIG. 3 andbefore releasing the substrate 100 illustrated in FIG. 4. Otherprocesses, such as implant or anneal processes, may also be performedwhile the surface of the substrate 100 is in a curved configuration.

FIGS. 6 and 7 illustrate embodiments similar to those discussed abovewith reference to FIG. 5, except that the embodiments disclosed in FIGS.6 and 7 utilize a concave processing surface. As noted above, theembodiments discussed above utilizing a convex processing surface may beparticularly useful in designing PMOS. For NMOS devices, similartechniques may be utilized wherein a concave processing surface isutilized.

For example, FIG. 6 illustrates an embodiment similar to thatillustrated in FIG. 5 in that stress-inducing regions 602 are formed inrecesses in source/drain regions of a substrate 100 while the substrate100 is in a curved configuration, except that the embodiment illustratedin FIG. 6 exhibits a concave processing surface. The substrate 100 maybe placed in a holder 606 for processing. In this example, when thesubstrate 100 comprises a silicon substrate, stress-inducing regions 602may be formed of SiC, which has a smaller lattice structure than thesilicon substrate 100. The lattice structure of the SiC stress-inducingregions 602 causes a tensile stress (indicated in FIG. 6 by arrows 608)in the channel regions, thereby increasing the electron mobility. SiCstress-inducing regions 602 may be epitaxially grown in a SEG processsuch as CVD using Si-containing gases, such as SiH₄, and C-containinggases, such as C₂H₄ or C₂H₆, as precursors.

FIG. 6 also illustrates an embodiment in that silicide regions 622 areformed while the substrate 100 is in a curved configuration, except thatthe embodiment illustrated in FIG. 6 exhibits a concave processingsurface. The silicide regions 622 may be formed in a similar manner asdiscussed above with reference to FIG. 5.

FIG. 7 illustrates the substrate 100 from FIG. 6 after the substrate 100has been released. As indicated by arrows 708, the stress-inducingregions 602 exert a tensile stress in the channel region greater thanthat obtained using similar processes and materials on a planar wafer,at least partially due to the epitaxial growth on the curved surfacedecreasing the volume of the recesses.

In some embodiments, the holders 212 (see FIGS. 2) and 606 (see FIG. 6)may comprise a vacuum to help secure the wafer. Embodiments including avacuum may be desirable wherein a concave processing surface is to beformed such that the vacuum may draw and hold a region of the substratelower than surrounding regions.

Additionally, the holders 212 and 606 are illustrated as beingcontinuous solid pieces for illustrative purposes only. In otherembodiments, the holders 212 and 606 may comprise ridges, posts, stands,or the like upon which a wafer may rest. Collectively, the ridges,posts, stands, or the like may provide a support surface having a convexor concave shape as discussed above. The holder may further accommodateheating structures, cooling structures, or the like.

FIGS. 8 and 9 illustrate other embodiments in which a curved processingsurface may be utilized. The configurations illustrated in FIGS. 8 and 9provide an example in which embodiments may be utilized with replacementgate (RPG) processing techniques. Generally, RPG processing techniquesinvolve forming a transistor utilizing a dummy gate structure. The dummygate structure is then removed and replaced with another gate structure.

Referring first to FIG. 8, there is shown the substrate 100 having aconvex processing surface with a patterned layer 830 formed thereon.Source/drain regions 802 may be formed in the substrate 100. Thepatterned layer 830 may be formed by forming a dummy gate electrode andforming a dielectric layer adjacent to the dummy gate electrode suchthat the dummy gate electrode is exposed. The dummy gate electrode maythen be removed, and the substrate placed in a configuration such thatthe processing surface of the substrate is convex as illustrated in FIG.8. The opening left by the dummy gate electrode may be filled with, forexample, a metallic material 834.

Excess material, if any, may be removed. In an embodiment, the substrate100 is released and returned to a planar or near planar configuration,and thereafter, excess metallic material may be removed using, forexample, a CMP process or a wet etch.

It is believed that devices formed using processes such as thosediscussed above may be useful in forming NMOS devices due to highertensile stress created in the channel region.

FIG. 9 illustrates an RPG process using a concave processing surface ofa substrate 100, which may be useful for forming a PMOS device. Similarmaterials, techniques, and processes as those discussed above withreference to FIG. 8 may be used in this embodiment, wherein likereference numerals refer to like elements, except that the processingsurface of the substrate 100 exhibits a concave shape rather than aconvex shape.

FIGS. 10 and 11 illustrate yet other embodiments in which a convex orconcave surface is utilized in combination with a stress memorizationlayer. Generally, a stress memorization layer is a layer having adifferent lattice structure than the underlying structures, such as thesubstrate, gate electrodes, or the like. The stress memorization layeris applied to the surface and an anneal process is performed, therebycausing the underlying structures to “memorize” the stress imparted bythe stress memorization layer.

Referring first to FIG. 10, there is shown the substrate 100 having aconvex processing surface with a stress memorization layer 1040 formedthereon. The stress memorization layer 1040 may be blanket formed,before or after a convex processing surface is formed. The stressmemorization layer 1040 may be a single layer, such as a single layer ofnitrides, oxynitrides, TEOS, other materials with internal stresses, orthe like, or a plurality of layers, such as a layer of an oxide and alayer of a nitride. The stress memorization layer 1040 may be formed by,for example, LPCVD, plasma enhanced chemical vapor deposition, or thelike. The stress memorization layer may be removed after performing ananneal. Embodiments such as that illustrated in FIG. 10 may beparticularly useful in fabricating, for example, NMOS devices.

FIG. 11 illustrates a stress memorization process using a concaveprocessing surface of the substrate 100, which may be useful forforming, for example, a PMOS device. Similar materials, techniques, andprocesses as those discussed above with reference to FIG. 10 may be usedin this embodiment, wherein like reference numerals refer to likeelements, except that the processing surface of the substrate 100exhibits a concave shape rather than a convex shape.

FIGS. 12 and 13 illustrate yet other embodiments in which a convex orconcave processing surface is utilized in formation of a fully strainedchannel (FSC). Referring first to FIG. 12, a stress-inducing region 1212is formed in a recess of a substrate 100. The recess and thestress-inducing regions 1212 may be formed in a similar manner asdiscussed above with reference to FIGS. 1-4, except whereas FIGS. 1-4formed recesses in the source/drain regions, the embodiment illustratedin FIG. 12 forms the recess 1210 in the channel region. The material ofthe stress-inducing region 1212 is selected such that a lattice mismatchexists between the material of the stress-inducing region 1212 and thematerial of the substrate 100. In an embodiment in which a PMOS deviceusing a silicon substrate is being formed, the stress-inducing region1212 may be formed of SiGe. When released, the stress-inducing region1212 may exert a compressive stress in the channel region greater thanthat obtained using similar processes and materials on a planar wafer,at least partially due to the epitaxial growth on the curved surfaceincreasing the volume of the recesses. Embodiments may be applied toplanar MOS technology or fin technology (e.g., FinFET).

FIG. 13 illustrates a similar embodiment as that illustrated in FIG. 12,except a concave processing surface is utilized rather than a convexprocessing surface. In particular, FIG. 13 illustrates the substrate 100having a stress-inducing region 1312 formed in a recess. In anembodiment in which an NMOS device is being formed and the substrate 100comprises a silicon substrate, the stress-inducing region 1312 may beformed of SiC, which has a smaller lattice structure than the siliconsubstrate 100, thereby causing a tensile stress in the channel regions.The SiC stress-inducing region 1312 may be epitaxially grown in a SEGprocess such as CVD using Si-containing gases, such as SiH₄, andC-containing gases, such as C₂H₄ or C₂H₆, as precursors. When released,the stress-inducing region 1312 may exert a tensile stress in thechannel region greater than that obtained using similar processes andmaterials on a planar wafer, at least partially due to the epitaxialgrowth on the curved surface increasing the volume of the recesses. Thestress-inducing region 1312 may also be formed of Si on SiGe bilayer orother III-V material or its multilayer. Embodiments may be applied toplanar MOS technology or fin technology (e.g., FinFET).

FIG. 14 illustrates a curvature that may be used in the embodimentsdiscussed above, in accordance with an embodiment. As shown, thesubstrate 100 may have a curvature having a radius of about 100 m toinfinity. In an embodiment in which the substrate 100 comprises a 300 mmwafer, the radius results in the substrate 100 having a curvature widthW of about 0 μm to about 1800 μm, as illustrated in FIG. 14. Thiscurvature width W may be an amount of curvature for either a concaveprocessing surface or a convex processing surface. Other wafer sizes,such as a 450 mm wafer, may also be used.

FIGS. 15A1-15D2 illustrate various topography patterns that may beapplied to a processing surface of a substrate, wherein darker regionsrepresent regions having a higher topography than lighter regions.Accordingly, FIGS. 15A1 and 15A2, wherein FIG. 15A2 is a cross-sectionalview along the A2-A2 line of FIG. 15A1, represent a topography in whicha horizontal center band 1510 is higher than upper and lower horizontalbands 1520, thereby creating a convex processing surface along the A2-A2line. FIGS. 15B1 and 15B2, wherein FIG. 15B2 is a cross-sectional viewalong the B2-B2 line of FIG. 15B1, illustrates a reverse of FIG. 15A,wherein a horizontal center band 1530 is lower than upper and lowerhorizontal bands 1540, thereby creating a concave processing surfacealong the B2-B2 line. FIGS. 15C1 and 15C2, wherein FIG. 15C2 is across-sectional view along the C2-C2 line of FIG. 15C1, represent atopography in which a center region 1550 is higher than a surroundingregion 1560, thereby creating a convex processing surface. FIGS. 15D1and 15D2, wherein FIG. 15D2 is a cross-sectional view along the D2-D2line of FIG. 15D1, represent a topography in which a center region 1570is lower than a surrounding region 1580, thereby creating a concaveprocessing surface.

FIGS. 16A1-16D3 represent various types of holders that may be used. Itshould be noted that the type of holder may be varied dependent upon thetopography being used. For example, FIGS. 16A1-16A3 correspond to typesof holders that may be used, for example, with the topographyillustrated in FIG. 15A; FIGS. 16B1-16B3 correspond to types of holdersthat may be used, for example, with the topography illustrated in FIG.15B; FIGS. 16C1-16C3 correspond to types of holders that may be used,for example, with the topography illustrated in FIG. 15C; and FIGS.16D1-16D3 correspond to types of holders that may be used, for example,with the topography illustrated in FIG. 15D.

FIGS. 16A1, 16B1, 16C1, and 16D1 represent holders utilizing pointcontacts, such as point contacts 1610. Embodiments utilizing topographyring such as FIGS. 16C1 and 16D1 may utilize more point contacts 1610than embodiments utilizing bands such as FIGS. 16A1 and 16B1.

FIGS. 16A2, 16B2, 16C2, and 16D2 illustrate holders utilizing contactbands 1612. As seen in FIGS. 16C2 and 16D2 that utilize peripheraltopography rings extending along a perhiphery having a differenttopography than a center region, contact bands 1612 may be utilizedalong both axis (e.g., horizontal and vertical) as compared toembodiments illustrated in FIGS. 16A2 and 16B2. FIG. 16B2 illustrates anembodiment in which contact bands 1612 are utilized along the horizontalaxis with a topography varying only along the vertical axis.

FIGS. 16A3, 16B3, 16C3, and 16D3 represent holders comprising contactrings extending completely around the substrate.

FIG. 16E illustrates yet another type of holder in accordance with anembodiment. In this embodiment, a pull force is applied by the holder.This type of pull force may be applied individually or in combinationwith another type of holder, such as those discussed above. Embodimentssuch as these may be used to form NMOS or PMOS devices. For example, apull force may be used to form the RPB for an NMOS device, while a pullforce may be used to form epitaxial layers in the source/drain regionsor the channel region (e.g., FSC) for a PMOS device.

The holders discussed above may be used to mount a wafer onto. Theholder may then be placed into one or more process chambers. In anembodiment, a cluster chamber tool may be used. Generally a cluster toolincludes a plurality of process chambers interconnected with a bufferchamber. The process chambers may perform similar processing or eachprocess chambers may perform different processing. For example, theprocessing chambers may be configured to perform epitaxial growth,annealing, silicidation, nitridation, CVD, PVD, and the like.Interconnected to the buffer chamber may be one or more loadlockchambers. The buffer chamber and the one or more loadlock chamberspermit transferring one or more wafers between the process chamberswithout breaking vacuum between processes or chambers.

The cluster tool may optionally further include a front-opening unifiedpod (FOUP) docking system and a factory interface. The FOUP dockingsystem and the factory interface allow wafers to be loaded and unloadedwithout exposing the loadlock chambers, the buffer chamber, and theprocess chambers to air. In operation, wafers are transferred into andout of the cluster tool, either individually or in batches, via the FOUPdocking system. The wafers are transferred from the FOUP docking systemto the loadlock chamber via the factory interface. Once transferred intothe loadlock chambers, the wafers are isolated from the ambientenvironment. The wafers are transferred to one or more of the processchambers.

In an embodiment, the wafer and the holder are inserted via the FOUPdocking system. The wafer mounted on the holder may then be transferredto one or more of the process chambers.

FIGS. 17A and 17B illustrate another method of forming a non-planar worksurface in accordance with other embodiments. Referring first to FIG.17A, there is shown the substrate 100 having a compressive stress film1712 applied to the backside of the substrate. The compressive stressfilm 1712 acts to create a convex processing surface along an opposingsurface of the substrate 100. After processing is completed, thecompressive stress film 1712 may be removed, thereby allowing thesubstrate 1710 to return to planar or near-planar.

In an embodiment, the compressive stress film 1712 may be formed ofSiGe, SiGeN, nitride, oxide, oxynitride, combinations thereof, and thelike, formed by a CVD process, a PVD process, an ALD process, or thelike. In an embodiment, the compressive stress film 1712 has a thicknessof about 10 nm to about 1000 nm, exerting a compressive stress fromabout 0.1 GPa to about 20 GPa.

Referring now to FIG. 17B, there is shown the substrate 100 having atensile stress film 1722 formed along a backside thereof. In thisembodiment, the tensile stress film 1722 is utilized to form a concaveprocessing surface. In an embodiment, the tensile stress film 1722 maybe formed of SiN, oxide, oxynitride, SiC, SiCN, Ni silicide, Cosilicide, combinations thereof, and the like, formed by a CVD process, aPVD process, an ALD process, or the like. In an embodiment, the tensilestress film 1722 has a thickness of about 10 nm to about 1,000 nm,exerting a compressive stress from about 0.1 GPa to about 20 GPa. Thetensile stress film 1722 may be removed after processing, therebyallowing the substrate 1710 to return to planar or near-planar.

In an embodiment, a method of forming a semiconductor structure isprovided. The method comprises providing a substrate, curving aprocessing surface of the substrate, and processing the substrate whilethe processing surface is curved.

In another embodiment, a method of forming a semiconductor structure isprovided. The method comprises providing a substrate comprising aprocessing surface such that the processing surface of the substrate hasa first curvature. The substrate is placed in a holder that isconfigured to maintain the substrate such that the processing surfaceexhibits a second curvature, the second curvature having a smallerradius than the first curvature. Thereafter, one or more process stepsare performed on the processing surface of the substrate. The substrateis removed from the holder, wherein upon removing the processing surfaceof the substrate exhibits a third curvature, the third curvature havinga greater radius than the second curvature. One or more additionalprocesses may be performed on the substrate.

In yet another embodiment, a substrate holder is provided. The holdercomprises one or more wafer support surfaces, the one or more wafersupport surfaces collectively being non-planar and one or moreconnectors configured to hold a wafer on the wafer support surfaces.

In yet another embodiment, a substrate holder is provided. The substrateholder includes a plurality of wafer contact points, at least one of theplurality of wafer contact points being non-planar with remaining onesof the plurality of wafer contact points, and one or more clamps along aperimeter of the plurality of wafer contact points, the one or moreclamps configured to secure a wafer on the plurality of wafer contactpoints.

In yet another embodiment, a substrate holder is provided. The substrateholder includes a plurality of wafer contact points, the plurality ofwafer contact points collectively forming a non-planar contact surface,and one or more clamps along a perimeter of the non-planar contactsurface, the one or more clamps configured to secure a wafer thenon-planar contact surface.

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutionsand alterations can be made herein without departing from the spirit andscope of the disclosure as defined by the appended claims. For example,different types of materials and processes may be varied while remainingwithin the scope of the present disclosure.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present embodiments, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present disclosure. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. A substrate holder comprising: one or more wafersupport surfaces, the one or more wafer support surfaces collectivelybeing non-planar; and one or more connectors configured to hold a waferon the wafer support surfaces.
 2. The substrate holder of claim 1,further comprising a vacuum port exposed to the wafer support surface.3. The substrate holder of claim 1, wherein the one or more connectorscomprise a continuous ring around a periphery of the one or more wafersupport surfaces.
 4. The substrate holder of claim 1, wherein the one ormore connectors comprise a plurality of point contacts.
 5. The substrateholder of claim 1, wherein the one or more wafer support surfaces form aconvex surface.
 6. The substrate holder of claim 1, wherein the one ormore wafer support surfaces form a concave surface.
 7. A substrateholder comprising: a plurality of wafer contact points, at least one ofthe plurality of wafer contact points being non-planar with remainingones of the plurality of wafer contact points; and one or more clampsalong a perimeter of the plurality of wafer contact points, the one ormore clamps configured to secure a wafer on the plurality of wafercontact points.
 8. The substrate holder of claim 7, wherein theplurality of wafer contact points collectively form a non-planar contactsurface, the non-planar contact surface having a non-linear surfacealong a first axis and a linear surface along a second axis.
 9. Thesubstrate holder of claim 8, wherein the second axis intersects a centerof the non-planar contact surface.
 10. The substrate holder of claim 9,wherein the center is higher than a periphery of the non-planar contactsurface along an axis perpendicular to the second axis and intersectingthe center.
 11. The substrate holder of claim 9, wherein the center islower than a periphery of the non-planar contact surface along an axisperpendicular to the second axis and intersecting the center.
 12. Thesubstrate holder of claim 7, wherein the plurality of wafer contactpoints collectively form a non-planar contact surface, the non-planarcontact surface having a peripheral region in a single plane and acentral region non-planar with the peripheral region.
 13. The substrateholder of claim 12, wherein the central region is higher than theperipheral region.
 14. The substrate holder of claim 12, wherein thecentral region is lower than the peripheral region.
 15. A substrateholder comprising: a plurality of wafer contact points, the plurality ofwafer contact points collectively forming a non-planar contact surface;and one or more clamps along a perimeter of the non-planar contactsurface, the one or more clamps configured to secure a wafer thenon-planar contact surface.
 16. The substrate holder of claim 15,wherein a periphery of the non-planar contact surface is planar.
 17. Thesubstrate holder of claim 15, wherein a periphery of the non-planarcontact surface is non-planar.
 18. The substrate holder of claim 15,wherein the one or more clamps comprise a first clamp and a secondclamp, the first clamp being on an opposing side of the non-planarcontact surface from the second clamp, the substrate holder being freeof other clamps.
 19. The substrate holder of claim 15, wherein the oneor more clamps comprise a first clamp, a second clamp, a third clamp,and a fourth clamp, the first clamp being on an opposing side of thenon-planar contact surface from the second clamp, the third clamp beingon an opposing side of the non-planar contact surface from the fourthclamp, the substrate holder being free of other clamps.
 20. Thesubstrate holder of claim 15, wherein the one or more clamps comprisemore than four clamps arranged around a periphery of the non-planarcontact surface.